1. Field of the Invention
The present invention relates to a toner for use in electrophotography. In addition, the present invention also relates to an image forming method, an image forming apparatus, and a process cartridge using the toner.
2. Discussion of the Background
For the purpose of improving quality of electrophotographic images, recently toners are being modified to have a smaller particle diameter. The smaller particle diameter a toner has, the lower fluidity the toner has. When a toner has poor fluidity, the toner tends to aggregate and transferability thereof deteriorates. As a result, hollow defects tend to occur in the resultant image. In particular, this phenomenon notably occurs in a toner including a release agent (such as a wax) so as to prevent occurrence of a paper winding problem and an offset problem. The paper winding problem is a phenomenon in which a transfer medium having a toner image thereon is wound around a fixing member or gets stuck to a separation pick, due to adhesion of the toner image thereto. The offset problem is a phenomenon in which a part of a fused toner image is adhered and transferred to the surface of a fixing member, and then the part of the toner image is re-transferred to an undesired portion of a transfer medium. Deterioration of transferability notably occurs in toners for use in full -color image forming apparatuses.
When the fluidity of a toner decreases, the occurrence of contact with a charge giving member (such as a carrier) decreases, and therefore the toner cannot be evenly charged. As a result, background fouling tends to occur in the resultant image. In particular, this phenomenon notably occurs in a toner including a release agent (such as a wax). Background fouling is a phenomenon in which the background portion of an image is soiled with toner particles which are not sufficiently charged, at a time when an electrostatic latent image formed on a photoreceptor is developed with a toner. Deterioration of chargeability notably occurs in toners for use in full-color image forming apparatuses.
In attempting to solve these problems, published unexamined Japanese patent application No. (hereinafter referred to as JP-A) 2004-151533 discloses an image forming apparatus including a charger comprising a conductive material having an Asker C hardness of not greater than 85° and a microhardness of not greater than 85° and using a developer (i.e., a toner) having a maximum elastic compressive load of from 15 to 70 mgf. It is described therein that such an image forming apparatus has a good and stable charging property.
JP-A 2005-266383 discloses a toner having a strength of from 0.1 to 1.0 kg/mm2 and a strength-displacement curve of which the ratio (kmax/kmin) of the maximum slope (kmax) to the minimum slope (kmin) is not less than 20, both determined by a micro compression testing machine. It is described therein that the abrasion amount of a cleaning blade can be reduced when such a toner is used, resulting in improving durability of the image forming apparatus used.
However, these toners tend to partially crack or transform when developed under a relatively high pressing force applied from a toner layer thickness controlling member in a one-component developing method, especially in a full-color image forming apparatus. As a result, the charge quantity of the toner changes and background fouling occurs in the resultant image.
On the other hand, in attempting to increase fluidity of a toner, toners are being modified to have a spherical shape. Since spherical toner particles easily pass through a cleaning blade when removed from the surface of a photoreceptor, the pressure of the cleaning blade needs to increase. In this case, the toner easily moves onto the surface of the photoreceptor due to the friction between the cleaning blade and the photoreceptor, resulting in the occurrence of black spots in the resultant image.
JP-A 2005-300937 discloses a spherical toner having a load-displacement curve having an inflection point, which is obtained by a micro compression test. It is described therein that such a toner has good mechanical stability, chargeability, transferability, and fixability. It is also described therein that when the inflection point appears in a load range of from 0.5 to 2 mN or the curve satisfies the following relationship through the inflection point:0.1≦d/P≦1wherein d (μm) represents the displacement and P (mN) represents the load, the toner is rapidly pressure-cracked in a fixing device and is prevented from fracturing and forming a film thereof in a developing device. Therefore, the toner has good chargeability, developability, and transferability. However, no detailed experimental result showing the relationship between the inflection point and the load is disclosed therein. Therefore, whether such a toner has the effect on the problem or not cannot be verified.